How Life May Have Begun on Earth

Cell Theory1. All living things are composed of

cells

2. Cells are the basic unit of structure and function in living things

3. New cells are produced only from existing cells

Q: How were the first cells developed?

Heterotroph hypothesis• An explanation for how early life

forms may have developed on the primitive Earth

Assumptions• Earth was hot

• Lots of inorganic substances–Hydrogen cyanide, carbon dioxide,

carbon monoxide, nitrogen, hydrogen sulfide, water

• Lots of energy

• Energy from the Earths environment helped create chemical bonds among particles in the seas

• This made the first organic molecules like sugars, amino acids, and nucleotides

Testing the Heterotroph Hypothesis

• Stanley Miller & Harold Urey built the “Miller Urey apparatus”

• This apparatus simulated the primitive environment

Miller Urey apparatus

More Testing of the Heterotroph Hypothesis

• Sidney Fox conducted further experiments that joined these organic compounds into aggregates, similar to “cell-like” structures

It is hypothesized that…

• Some of the large complex molecules formed aggregates which probably incorporated molecules from the seas as “food”

Q: What kind of nutrition is this?

A: Heterotroph

• In time, these aggregates became increasingly complex and organized

• These aggregates are considered to be “alive” when they develop the ability to reproduce

How modern day Earth conditions were thought to be created

• It is thought that these heterotrophs evolved a pattern of respiration similar to the anerobic process of fermentation

Fermentation

Pyruvic Acid + NADH alcohol + CO2 NAD+

How modern day Earth conditions were thought to be created

• Some heterotrophs evolved a means of using carbon dioxide to synthesize organic compounds

CO2 + H2O +C6H12O6 O2light

(Carbon Dioxide) (Water) (Sun) (Glucose) (Oxygen)

Q: What kind of nutrition is this?

A: Autotroph

With a Partner• Do questions 5, 11, 21, 34, 35, 36

in your review books